UN Secretary General Kofi Annan has warned that swift action must be taken over the security situation in Darfur or intense violence could break out.

In a report to the Security Council, he said groups were re-arming and violence was spreading beyond the region.

He called on the Sudanese government and rebels to reconvene political talks in a spirit of reconciliation.

Khartoum-backed militia are accused of killing thousands as part of a campaign against rebels demanding more rights.

Every month, the UN's reports on Darfur paint an increasingly bleak picture and this one is no exception.

Mr Annan said the build-up of weapons and intensification of violence, including air attacks, suggested the security situation in Darfur was deteriorating.

He said both the government and rebels had repeatedly violated the ceasefire agreement, and the government had started a massive build-up of forces and logistics.

Sanctions threat

The continuing violence has led to yet more people being displaced and increasing problems for aid agencies trying to reach the vulnerable in north and south Darfur.

The secretary general said the Sudanese government was not taking any action to bring militia leaders accused of widespread killings to justice, and instead was once again including them in military operations.

Mr Annan said the two sides had failed to use the momentum offered by the agreement between rebels in the south and Khartoum, which is due to be signed on Sunday.

He said they now had to be persuaded by a combination of pressure and assurances from influential member states that it was in their interests to pursue a settlement through peaceful means.

The Security Council has passed two resolutions threatening sanctions against Sudan if the violence, which has led to the deaths of tens of thousands of people, does not end.

But the members are unable to agree on the next step.

Mr Annan's report will be discussed by the Security Council early next week.